Bifurcated endovascular stents and method and apparatus for their placement

ABSTRACT

A bifurcated endovascular stent is formed from a pair of individual tubular component stents that can be placed independently in sequence in the branched region of a body vessel to form the bifurcated stent in situ. The first placed component stent includes a side opening and may be placed to extend both proximally and distally of the bifurcated junction with the side opening facing the entry to the branch vessel. The first component stent then is expanded within the vessel. The second component stent then can be advanced through the first component stent, through the side opening and into the branch vessel where it can be expanded. The portions of the first and second component stents that surround the region of the vessel juncture are constructed to provide enhanced lateral support for the walls of the vessel in the region of the junction. A delivery catheter is provided and includes a guidewire duct adapted to facilitate entry of a guidewire into the branch vessel while the first component stent is being deployed in the other lumen of the vessel.

TECHNICAL FIELD

The present invention relates to bifurcated endovascular prosthesisimplantable in a passage of the human or animal body and to the relativemethod and apparatus for their placement, prosthesis that are commonlyreferred to as "stents".

BACKGROUND OF THE INVENTION

A number of medical procedures involve or can be supplemented with theplacement of an endoluminal prosthesis, commonly referred to as a stent,that can be implanted in a lumen, such as a blood vessel or othernatural pathway of a patient's body. Such stents typically define agenerally tubular configuration, and are expandable from a relativelysmall diameter (low profile) to an enlarged diameter. While in its lowprofile configuration, the stent is advanced endoluminally, by adelivery device, through the body lumen to the site where the stent isto be placed. The stent then can be expanded to a larger diameter inwhich it can firmly engage the inner wall of the body lumen. Thedelivery device then is removed, leaving the implanted stent in place.In that manner, the stent may serve to maintain open a blood vessel orother natural duct, the functioning of which had become impaired as aresult of a pathological or traumatic occurrence.

Among the medical procedures in which stents have had increasing use isin connection with percutaneous transluminal angioplasty (PTA), andparticularly percutaneous transluminal coronary angioplasty (PTCA). PTAand PTCA involve the insertion and manipulation of a dilating catheterthrough the patient's arteries to place the dilatation balloon of thecatheter within an obstructed portion (stenosis) of a blood vessel. Theballoon then is expanded forcibly within the obstruction to dilate thatportion of the blood vessel thereby to restore blood flow through theblood vessel. Among the more significant complications that may resultfrom such angioplasty is that in a significant number of cases, thedilated site again becomes obstructed. By placing a stent within theblood vessel at the treated site, the tendency for such restenosis maybe reduced.

Stenoses often may develop in the branching region of a patient's bloodvessel. Treatment of a stenosis in the branched region may presentnumerous additional difficulties in the design of devices to dilatestenoses at the branched region.

A number of stents have been proposed and developed in the art,including single stents that define a single luminal pathway as well asbifurcated stents that define a branched pathway and are intended to beplaced in a branching region of a blood vessel. The development ofbifurcated stents, as compared to single stents, presents numerousdifficulties because of the branched arrangement and the difficulty indelivering and placing a bifurcated stent at the branched region of ablood vessel.

In one arrangement, disclosed International Application No.PCT/IB96/00569, filed Jun. 7, 1996, entitled "Bifurcated EndovascularStent" a bifurcated stent is formed from two, initially independent,component stents. In the preferred embodiment each component stent isformed from wire and has an elongate spine and a plurality of generallytube-defining modules connected to the spine in a longitudinallysequenced array. Each component stent defines a generally tubularconfiguration. The modules on the two component stents are arranged toenable them to be combined, in situ, to form a bifurcate configuration.Each component stent may be considered to have a proximal set of modulesand a distal set of modules. The modules in the proximal set of onecomponent stent are arranged longitudinally to enable them to beinterfitted with a complementary module set on the proximal end of theother component stent.

The device is placed at the vessel bifurcation by first inserting one ofthe component stents to place its proximal module set in the commonblood vessel and its distal module set in one of the branches of theblood vessel. The first placed component stent is provided with a sideopening between its ends and is placed so that the side opening ispositioned at the juncture of the blood vessels to provide access to thebranch vessel. The modules in the first component stent then areexpanded to secure the first component stent in place. The secondcomponent stent then can be advanced into and through the firstcomponent stent and transversely through the side opening of the firststent to project the distal module set of the second component stentinto the second branch of the blood vessel. With the second componentstent so placed, and with its proximal module set aligned to fit incomplementary fashion with the proximal module set of the firstcomponent stent, the second component stent can be expanded in place.

The present invention is directed to an improved method and apparatusfor placing the component stents in a bifurcated configuration in abranched vessel. A further object of the invention is to provideimprovements in stent construction by which the stent can providesubstantially continuous support for the vessel, including the region ofthe vessel junction.

DISCLOSURE OF THE INVENTION

In one aspect of the invention, a delivery catheter is provided todeliver and position the first component stent so that the side openingbetween the proximal and distal module sets is disposed at the junctureof the common and branch blood vessels with the side opening beingexposed to the entrance to the branch vessel. The delivery catheterincludes a shaft with a stent expansion means, such as a balloon, at itsdistal end. The first component stent is mountable, in a low profile, onthe expansion means. The delivery catheter also includes an elongatetubular guidewire duct that extends along and parallel to the cathetershaft, the distal end of the guidewire duct terminating at about themidportion of and lying exteriorly of the balloon. When the firstcomponent stent is mounted on the delivery catheter, it is disposedabout the balloon and with the distal region of the guidewire duct beingdisposed in registry with the side opening of the first component stent.

With the first component stent mounted on the balloon, the catheter canbe navigated through the patient's vasculature to place the stent at thevessel bifurcation with its proximal module set disposed in the commonblood vessel and the distal module set disposed in one of the branchesbeyond the junction. The catheter is manipulated into a position, aswith the use of a conventional guidewire, so that the side opening is inregistry with the lumen of the other branch vessel. When so positioned,a second guidewire is advanced through the guidewire duct and emergesinto the branch vessel through a guidewire port at the distal end of theguidewire duct. The expansion means then is operated to expand the firstcomponent stent into firm engagement with the blood vessel. Theexpansion means then can be deactivated and the delivery catheter can beremoved from the patient while maintaining the second guidewire in placein the branch vessel. The second component stent, mounted on a balloondelivery device then can be mounted on a delivery device that can beadvanced along the second guidewire to guide the delivery device (e.g.,a balloon catheter) into the first component stent and laterally throughthe side opening of the first component stent and into the branch bloodvessel. The second component stent is positioned so that its proximalmodule set is aligned in complementary configuration with the proximalmodule stent of the first component stent. The second component stentthen can be expanded to engage its proximal module set with that of thefirst component stent and to deploy the distal module set in the branchvessel. The first and second component stents, so placed, cooperate todefine a bifurcated stent structure for supporting branched bloodvessels.

In another aspect of the invention, the modules of one or both of thecomponent stents that are disposed immediately at the juncture of theblood vessel are formed to provide lateral support for the junctureregion of the blood vessels.

Among the objects of the invention is to provide an easily placeablebifurcated endovascular stent.

Another object of the invention is to provide a bifurcated stent thatcan be placed in the coronary arteries as well as other branchedvessels.

Another object of the invention is to provide a bifurcated stent formedfrom component stents that can be constructed in situ in the branchedregion of a patient's vasculature.

An additional object of the invention is to provide an endovascularstent that is formed from two generally tubular members, at least one ofwhich has a side opening between its ends to enable part of anotherstent to be passed partly through the first stent and transversely outof the side opening.

Another object of the invention is to provide a bifurcated stent thatcan be custom tailored to the vascular anatomy of the patient in whomthe device is to be implanted.

A further object of the invention is to provide a bifurcated vascularstent having good radiographic characteristics to facilitate itsplacement and subsequent visualization of the stent.

A further object of the invention is to provide a delivery catheteradapted to facilitate placement of a first component stent that extendsinto one branch vessel and a guidewire that extends into the otherbranch vessel and along which a second component stent can be directedinto the other branch vessel.

Another object of the invention is to provide complementary componentstents that when placed in the blood vessel provide substantial stentingsupport in the region of the juncture of branched blood vessels as wellas in the branches themselves.

DESCRIPTION OF THE DRAWINGS

The foregoing and other objects and advantages of the invention will beappreciated more fully from the following description thereof, withreference to the accompanying drawings wherein:

FIG. 1 is an illustration of the distal end of a delivery catheter forplacing the first component stent in one of the branch vessels and aguidewire in another branch vessel;

FIG. 2 is a fragmented illustration of a portion of a component stentillustrating a pair of adjacent modules connected to a spine;

FIG. 3 is an enlarged illustration of the encircled region of FIG. 6showing the junction region of branched blood vessels and the manner inwhich the component stents cooperate at that juncture;

FIGS. 4a-4g illustrate, in longitudinal section, the successive steps bywhich the first and second component stents may be placed to form thebifurcated stent;

FIG. 5 is a longitudinal sectional illustration of a branched bloodvessel in which a first component stent has been placed;

FIG. 6 is an illustration similar to FIG. 5 in which the secondcomponent has been placed; and

FIG. 7 is a diagrammatic illustration of another stent expansion meansutilizing electrical energy for causing expansion of the stent;

FIG. 8 is a side view of a first component stent in another embodimentof the invention;

FIG. 9 is a side view of a second component stent adapted forcomplementary association with the component stent of FIG. 8;

FIG. 10 is a side view of the first and second component stents of FIGS.8 and 9 assembled to form a bifurcated stent in a bifurcated bodyvessel;

FIG. 11 is an illustration of another embodiment of a component stentwith the modules developed in a horizontal plane better to illustrate anarrangement for defining a side opening in the component stent;

FIG. 12 illustrates a bifurcated endovascular stent formed and in placewithin a bifurcated blood vessel and incorporating the construction ofFIG. 11;

FIG. 13 illustrates further details of a module in the stent shown inFIG. 12; and

FIG. 14 illustrates a pair of modules of the arrangement as shown inFIG. 12.

DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

FIGS. 2 and 5 illustrate the type of modular endoprosthesis 1 (stent)that may be used in practicing the invention. The endoprosthesis may beconsidered to define a cage-like tubular arrangement 10 formed fromwire-like components and having a central longitudinal axis 2. The stent1 is constructed from a plurality of individual modules 7 connected toeach other along a spine that may be considered to include alongitudinal support wire 6 and connectors 9. The modules 7 areexpandable from a contracted, low profile configuration (FIG. 4a), tofacilitate placement of the stent in the body lumen, to an enlargeddiameter, as suggested in FIG. 4b, in which the modules can be broughtinto firm engagement with the inner surface of walls 11 of the bodylumen 3 to maintain the body lumen open to facilitate blood flow. In thepreferred embodiment, the modules are expandable inelastically. Theradially expandable, generally tubular, modules 7 are mounted andaligned in longitudinally sequenced array on the support wire 6 by aconnector 9 associated with each of the modules 7. The modules, whenmounted on the support wire 6, may be considered to define a virtualperipheral surface 12 that, in transverse cross-section, is in the formof a virtual closed curve or loop 8 about the longitudinal axis 2.

Each module 7 is formed from a wire 13 shaped and configured to enableradial expansion of the cylindrical peripheral surface 12. The modulemay be formed by first forming the wire 13 into a flat serpentineconfiguration and then wrapping the serpentine wire into its loopedconfiguration. The terminal ends of the serpentine wire are free. Thefree ends of the wire 13 may be attached to each other and to thesupport wire 6 by the connector 9. The serpentine arrangement of each ofthe modules may be considered to include a series of elongate segments14 alternated with and connected by bends that may be curved (e.g.,circular) or may comprise shorter connective segments 15 connected tothe elongate segments 14 at cusps 17. The connective bends between thelongitudinal segments 14 may lie along and define a locus of the closedloop 8. Preferably, the wire 13 is formed so that the arrangement ofbends will be uniformly circumferentially spaced about the virtualclosed loop 8 to provide the modules 7 with uniform strength indirections transverse to the support wire 6.

When the modules are in their low profile, unexpanded configuration, thebends 15, 17 that define the connection between adjacent longitudinalsegments are such that the elongate segments 14 will lie substantiallyparallel to each other, defining an angle close to zero degrees. Theangle will increase when the module is expanded. The configuration ofthe connective bends, including the cusps 17 may be varied to vary theangle or to vary their number circumferentially about the closed loop 8to vary the characteristics of the modules 7, including varying itsresistance to compressive radial loads such that the endoprosthesis canfurther be tailored and made to conform ideally to the specific bodylumen 3 in which it is to be implanted.

By way of illustrative example only, a stent may be provided to includemodules 7 formed from wire having a diameter of about 0.15 millimeterwith elongate segments 14 (not including the connective bends betweenadjacent segments 14) of a length of about 1.8 millimeters. When theconnective bends between adjacent elongate segments 14 are smoothlycurved, they may have a radius of about 0.15 millimeter beforeexpansion. A stent having the foregoing dimensions can be expected to beexpandable to diameters between about 2.5 to about 4.0 millimeterswithout excessive expansion, and that such stent exhibits substantialresistance to radial collapse that is well above the maximum radialcompressive loads and can be expected to be imposed on the stent bycontraction of an artery having a luminal diameter of about 2.5 to about4.0 millimeters.

In the preferred embodiment the connectors 9 may be constructed to bemounted on the longitudinal support wire 6 as by threading them on thewire 6. The connector 9 preferably may comprise a small tube or ringthat defines sufficient internal space to receive and circumscribe thefree ends of the wire 13 while also permitting firm connection of thering to the longitudinal support wire 6. The ring connector 9, free endsof the wire and support wire 6 may be firmly connected by means of apermanent deformation, for example, by crimping, or may be attached toeach other by spot welding. When assembled using laser spot welding, itis preferred that the free ends of the wire 13 of the module 7 are firstwelded to the ring 9 and the ring 9 then is welded to the support wire6. In some instances, it may be desirable to modify the stent so thatone or more of the modules (but not the endmost modules) are notsecurely attached to the support wire but, instead, are permitted somefreedom of sliding movement along the support wire. This may enablemaking of a final adjustment to the position of the module after thedevice has been placed in the patient's blood vessel, should that bedesired.

The ring connector 9 may be in the form of a relatively short segment ofa tube receptive to the support wire 6 and the free ends of the module7. The internal surface of the ring connector 9 may be contoured toclosely match the contour defined by the support wire 6 and free ends ofthe wire 13 that pass through the connectors 9.

The foregoing construction enables a stent to be specially assembled toconform precisely to the specific anatomy of the patient in whom thestent is to be placed. The modules can be positioned as desired alongthe support wire 6 and can be secured in that configuration. The supportwire 6 may be selected to provide the desired degree of longitudinalflexibility and may be made from wire that is extremely flexible tofacilitate positioning of the device in relatively inaccessible bodylumen. With the foregoing construction in which the stent has anindependent support wire 6, the degree of stiffness or flexibility ofthe support wire can be selected independently of the wire from whichthe tubular modules 7 are formed. The support wire 6 may be highlyflexible to enable the stent to be carried through narrow, tortuousvessels, such as coronary arteries.

It should be understood that although the presently preferred embodimentof the invention incorporates a metal support wire 6 (e.g., stainlesssteel), the modular construction of the invention enables a fabricationof a stent in which the support wire may be formed from non-metallicmaterials, such as polymeric materials, for example, nylon or abiologically absorbable material. Other mechanically and biologicallysuitable classes of materials may be selected, including materials fromamong those that are biologically absorbable into the tissue of thevessel wall over time. With a bioabsorbable support wire 6, it should beselected to maintain its desirable mechanical characteristics for asufficient time to enable the modules 7 to become firmly embedded in thevessel wall. The stent modules can be formed from a shape memorymaterial such as a nickel titanium alloy (nitinol) by which theexpansion of the module can be effected by a resistance heating element105 (FIG. 7). Thus, the modular construction of the invention provides asubstantially increased range of materials and properties for theindividual components, each being selected to provide optimum results.The components of the stent may be coated with a protective materialsuch as carbon or with anticoagulant materials such as heparin. Suchvariations in materials enables balancing the mechanical strength andthe elastic yield of the tubular structure 10 in a manner to enable thestent to be adapted to specific needs of an individual patient.

The ring connectors 9, especially when assembled about the two endsegments of the modules 7 and the support wire 6, present asignificantly greater mass than that of the wire 13 from which themodules are fashioned. Thus, the region of the spine that includes thering connectors 9 will present substantially greater radiopacity thanthat presented by the wire 13 of the associated module. Thesubstantially increased radiopacity of the connected region enhancessubstantially the radiographic control of the endoprosthesis 1 duringimplantation. It also enables the prosthesis to be observedradiographically at a later time without requiring use of ultrasoundprocedures. The configuration of the stent enables the tubular frame 10to be constructed to have a high mechanical strength while enablingexpansion of the device between its low profile and maximum expandedconfiguration yet in which the wire 13 of the modules 7 will besubstantially transparent to X-rays at radiation levels that aretypically used in such procedures.

FIGS. 5 and 6 illustrate the placement spacers 50 between pairs ofsuccessive connectors 9 before the connectors are secured to the supportwire 6. The spacers preferably are cylindrical in shape and have acentral hole by which they can be slid, in bead-like fashion, onto andalong the longitudinal support wire 6. When a series of connectors 9 andspacers 50 have been placed on the support wire 6, each successive pairof connectors 9 or spacers 50 may embrace one of the other. The lengthof the spacer(s) may be predetermined to enable precise control over thespacing between two successive modules as well as to reduce the risk ofthe support wire 6 being twisted or otherwise becoming damaged. In mostcases, the spacing of adjacent modules desirably will be such that theycan be disposed in close proximity (e.g., with their cusps 17 adjacenteach other) to provide substantial continuous support to the vessel wall11 when the stent has been placed in the patient. Additionally, use ofthe spacers 50 enables a stent to be assembled with only the two endmostconnectors 9 anchored securely to the support wire 6. In such anembodiment, the intermediate components (the connectors 9 and spacers50) will be retained in position on the support wire and will notseparate. Whether all or only the endmost connectors 9 are secured tothe longitudinal support wire, the intermediate spacers need not bedirectly secured to the wire 6 but, instead, can be retained in place byand between their adjacent connectors 9. By way of dimensional example,the cylindrical spacers 50 that may be used with the device having theabove-described dimensions may be about 1.10 millimeters in length, 0.30millimeter in outer diameter and having a wall thickness of about 0.075millimeter.

The spacers 50, being circular in cross-section, may be arranged to liesubstantially flush with the rounded outside face of the adjacentconnecting elements. A further advantage in the use of spacers 50 isthat together with the ring connectors 9 and the portions of the wirethat extend through the rings, the arrangement defines a spine thatpresents a substantially continuous elongate mass having a radiopacityconsiderably greater than that of the serpentine wires 13.

All components of the device should be formed from materials that arecompatible with each other and will not form microcells that might giverise to electrochemical corrosion of any part of the device after it hasbeen implanted into the blood vessel. The longitudinal support wire 6,wire 13 and connector 9 preferably should have the same chemicalcomposition or compositions that are biologically compatible with eachother. Exemplary materials that are preferable in making theendoprosthesis include those from the group of annealed stainlesssteels, titanium alloys, gold-nickel alloys, nickel-chromium alloys, andtitanium-chromium alloys.

The support wire 6 and modules 7 may be treated and formed to vary themechanical and functional characteristics independently of each other toobtain a desired configuration adapted to treat the anatomy of aspecific patient. For example, the wire 13 from which the module isformed may be subjected to an annealing heat treatment to control themalleability of the wire.

FIGS. 5 and 6 illustrate the manner in which a bifurcated stent can beplaced in branched blood vessels. In this embodiment, the bifurcatedstent is formed from two single (i.e., non-bifurcated) component stents1P (FIG. 5) and 1S (FIG. 6). The first component stent 1P may beconstructed in the manner described above, to include an elongate spineto which a plurality of radially expandable modules 7 are attached. Themodules 7 of the stent 1P may be considered to be arranged in sets,including a first (proximal) set 1Pa that may be at the proximal end ofthe stent 1P and a second (distal) set 1Pb at the other end. The modules7 in the first set 1Pa are spaced along the spine at predeterminedintervals. As described in further detail below, the distance L betweenthe adjacent modules 7 in the first set 1Pa should be sufficient toenable the modules 7 of another stent to be fitted in between themodules 7 in the first set 1Pa. In the preferred embodiment, thepredetermined distance is not less than the length LM of one module 7measured along a direction parallel to the spine. The modules 7 in thesecond set 1Pb may be arranged in close longitudinal proximity to eachother or other spacing that may be appropriate for the particular branchof the vasculature into which it is to be placed. The first componentstent 1P also is constructed to have a space 1Pc that defines a sideopening SF between the first and second sets 1Pa, 1Pb of module 7. Theside opening SF enables a second component stent, in a low profileconfiguration, to be passed through the first component stent (afterexpansion of the first component stent) and protrude transversely out ofthe space 1Pc. By positioning the side opening SF at the juncture of thebranched blood vessels, a second component stent can be advanced intothe branch artery 3c. In a preferred embodiment, the length of the sideopening SF may be approximately that of the diameter 3s of thecross-section of the branch passage 3c. The modules 7 in the first setalso may be interconnected by a second longitudinal spine wire 6P, asmay be the modules in the second set 1Pb of the first component set 1P.When two spine wires are used, the continuity of the second spine wire6P (located uppermost as seen in FIG. 5) is interrupted for the lengthof the side opening SF between the module sets 1Pa and 1Pb. The secondcomponent stent preferably is provided only with a single longitudinalspine wire 6s. The stent can be built in situ in the patient by firstplacing and expanding the first component stent 1P with the side openingSF in registry with one of the branches 3c of the body lumen and theninserting the second component stent 1S through the first componentstent 1P and transversely through the side opening SF into the otherbranch lumen 3c. The proximal ends of the component stents preferablyare configured to cooperate with each other to define a common singletube.

The first stent 1P may be delivered to and placed in the artery by adelivery device, described below, having an expansion member that mayinclude a balloon 104. The first stent 1P is mounted on the balloon 104in a low profile.

The construction of the first component stent 1P includes thearrangement of the spine that may be considered to be defined by thelongitudinal support wire 6 and connectors 9. Spacers 50 also may beprovided between adjacent pairs of connectors 9. The pattern ofconnectors 9 or connectors 9 and spacers 50, may be configured to permitdistinct radiographic visualization of the space 1Pc at the intermediateportion of the stent to facilitate locating that portion at the desiredplace in the vascular branched region.

It may be noted that in the illustrative embodiment, the region of theside opening SF in the first component stent 1P is radiographicallydistinguishable from the other portions of the stent. In theillustrative embodiment that is achieved by omitting spacers or otherradiographically observable components along that portion of the spinethat extends between the proximal and distal module groups 1Pa, 1Pb.Thus, the spine, in the region 1Pc, is defined only by the support wire6 which has substantially less mass than the other portions of the spineso that that region can be radiographically distinguished.

The second component stent 1S may be of similar construction to thefirst component stent 1P, including a first set 1Sa of modules 7 spacedlongitudinally to interfit with the spaces between the modules in thefirst set 1Pa of the first component stent, and a second set of modules1Sb that may be arranged in close proximity to each other. The first andsecond module sets 1Sa, 1Sb may be separated by a space 1Sc of a lengthapproximating the diameter of the cross-section 3s of the branch passage3c. The second component stent may be placed, as described below, by aballoon delivery catheter after at least the first set of modules 1Pahas been expanded into secure engagement with the inner surface of theblood vessel 3. The second component stent 1S is placed longitudinallywithin the vasculature so that the modules 7 of the proximal set 1Sa ofthe second component stent is longitudinally aligned with the spacesbetween the modules 7 on the first set 1Pa of the first component stent1P. The relative positioning between the sets of modules may befacilitated by the radiopaque portions of the spine, particularly theregion of the connectors 9 and, if employed, the spacers 50. With themodules of the first set 1Pa, 1Sa aligned, the modules 7 on the secondset may be expanded. The resultant bifurcated stent structure may beconfigured to define a substantially continuous proximal stent portionwithin the blood vessel. Similarly, the second sets 1Pb, 1Sb of module 7are expanded into firm engagement with the portions of the blood vesselbranches in which they are placed.

In order to enhance the support for the vessel wall 11 at the junctureof the blood vessel branches 3, 3c, either one or both, of the componentstents 1P, 1S may be provided with specially constructed modules 7 that,when placed, will border the side opening SF. In such modified modules7, the longitudinal portions 14, 14' that define the virtual peripheralsurface 12 may be formed to have dissimilar lengths so that they mayextend into and provide greater support in the region of the juncture,particularly laterally of the region defined by the side opening SF.Thus, the modules 7 at the region of the vessel juncture may beconsidered to define a virtual cylindrical surface that includes alongitudinally projecting tongue 108 portion of the virtual cylindricalsurface thereby to provide additional support for the wall of thejuncture but without obstructing the side opening SF. Alternately, onevirtual cylinder defined by such a module may be considered to define avirtual surface that is oblique to the longitudinal axis 2 and isdefined by the cusps 17 of the module set. Thus, the end modules of eachof the modules sets 1Pa, 1Pb in the first component stent 1P may bearranged so that their cusps 15 can be disposed in close proximity toeach other. If desired, the tongues of the module 7 may interleave andalternate with each other as suggested in FIG. 3 at 108a. In thismanner, the wall 11 of the affected vessels can be better supported withlittle or no break in continuity along the length of the passage.Similarly, enhanced support may be provided in the region of thejuncture associated with the branch passage 3c by providing a tongue108' on the module 7 of the second component stent 1S disposed at thejuncture of the branch passage 3c. The balance between the mechanicalstrength of the stent 1 and its ability to yield elastically can beoptimized further by fashioning the module 7 with the tongue 108 or 108'from a wire 13 having a diameter different from that of the wire usedfor other of the modules or, alternately, by subjecting the modules tosuitable heat treatment before their assembly into the stent.

FIG. 1 illustrates a delivery catheter particularly adapted to deliverand place the first component stent of the bifurcated stent inaccordance with the invention. It should be understood that although thecatheter 100 is illustrated as including an expansion means in the formof an inflatable balloon 104, other expansion means, for example only,an electrical resistance heater 105 (FIG. 7), may be employed. Thedelivery catheter 100 may have a coaxial shaft including an inner tube101 disposed within an outer tube 110. The inner tube 101 extendsthrough the balloon to a terminal portion 100t and is open at its distalend. The ends 104e of the balloon are secured to the distal end of theinner and outer tubes 101, 110, as is conventional in coaxial ballooncatheters. The annular space defined between the inner tube 101 and theouter tube 110 defines a first lumen through which the balloon can beinflated and deflated. The lumen (defined as second) through the innertube 101 receives a guidewire G1 to facilitate navigation of thecatheter 100.

The delivery catheter also includes an elongate tubular guidewire duct102 that extends along the catheter shaft and has a distal portion 102dthat terminates short of the distal portion 101d of the inner tube 101.The distal end of the guidewire duct 102 is formed to include an exitport 102e oriented to enable a second guidewire G2 to protrude laterallyaway from the catheter 100. The expansion means, e.g., the balloon 104,is mounted to the catheter so that the guidewire port 102e at the distalportion 102d of the guidewire duct 102 remains exposed. When the stentis loaded onto the catheter, the balloon is folded, as by two folds 106,fashioned to embrace the guidewire duct 102. Alternately, the guidewireduct 102 could be directed through the inflation first lumen 110 andemerge marginally before the point where the balloon is secured assuggested in phantom in FIG. 1. As described below in further detail,when the device is placed in the patient, a second guidewire G2 can beadvanced through the guidewire duct 102 and projected laterally throughthe guidewire port 102e and advanced into the branch passage 3c. It willbe appreciated that when the stent is fitted onto the balloon, thedistal section 102d of the guidewire duct 102 will be captured betweenthe stent and the balloon. The guidewire port 102e is disposed relativeto the stent so that it will be in registry with the side opening SF ofthe first component stent.

When the expansion means includes an electrical resistance heater 105,preparation of the catheter 100 may comprise the step of locating theheater 105 between the first and second tubes 101, 102 (FIG. 7).

The stent 1 may be fitted on the distal end of the catheter by a loadingdevice such as that described in International Application No. PCT/IB96/00918, filed Sep. 13, 1996, entitled "Device and Method for Mountingan Endovascular Stent Onto a Balloon Catheter" to which reference ismade. The placement and creation of the bifurcated stent, in situ, isillustrated in the sequential drawings of FIGS. 4a-4g. Typically, beforethe component stents 1P, 1S are placed in the blood vessel, anangioplasty procedure is performed in the blood vessels 3, 3c. Thedelivery catheter will first be set up with the first guidewire G1extending through the inner tube 101 of the catheter shaft. The firstcomponent stent 1P then is fitted to the catheter 100 about theexpansion means 104, 105, with the guidewire port 102e of the guidewireduct 102 in registry with the side opening SF. The catheter 100 then isinserted into the patient's blood vessel and is advanced, along with andwith the aid of the guidewire G1 to locate the assembly with theguidewire port 102e disposed at the juncture of the blood vesselbranches and facing the branch passage 3c (FIG. 4a). The secondguidewire G2 then is inserted into the guidewire duct 102, advancing theguidewire G2 so that its tip emerges from the guidewire port 102e. Theguidewire G2 then is advanced into the branch passage 3c (FIG. 4b). Theexpansion means 104, 105 then is operated to expand the first componentstent 1P and stabilize its position in the blood vessel 3 (FIG. 4c). Thecatheter 100 and guidewire G1 then may be withdrawn from the bloodvessel 3 while maintaining the second guidewire G2 in its positionwithin the branch passage 3c (FIG. 4c). The second component stent 1Sthen is fitted to the same or another catheter in a low profile. Thatcatheter then is advanced along the second guidewire G2 until the secondcomponent stent 1S and particularly the second set 1Sb of modules 7 isdisposed in the branch passage 3c (FIG. 4d). The expansion means 104,105 then is operated to expand and stabilize the second component stent1S within the branch passage 3c and the main passage 3 (FIG. 4e). Thesecond catheter then may be deflated and withdrawn (FlG. 4f). The secondguidewire G2 also is withdrawn (FIG. 4g).

It should be appreciated that because of the relative ease by which theconnecting elements 9 of the spine can be fluoroscopically monitored,the first and second component stents can be aligned and oriented withrespect to each other in the blood vessels. The use of a double spinefor the first component stent 1P enhances this ability. A single spineis preferred for the second component stent 1S. The radiopacity of thesingle spine enables the physician to locate the second component stent1S to interpose the modules 7 of the first sets 1Pa and 1Sa and with thesingle longitudinal wire 6 of the second component stent is rotated 90°in relation to the two spines of the first component stent, all parts ofthe prosthetic structure are readily identifiable (see FIGS. 4d-4g).

FIGS. 8-10 illustrate a variation of the invention. FIGS. 8-10incorporate reference numerals in a similar pattern of that of theembodiment illustrated in FIGS. 5 and 6 but with the addition of "200"to the reference numeral. Thus, as shown in FIGS. 8-10, the features ofthe invention and their reference numerals are as follows:

    ______________________________________                                        space (between two modules)                                                                              200sv                                              stent                      201                                                first component stent      201P                                               proximal module set of first component stent                                                             201Pa                                              distal module set of first component stent                                                               201Pb                                              space (between proximal and distal module sets)                                                          201Pc                                              second component stent     201S                                               proximal module set of second component stent                                                            201Sa                                              distal module set of second component stent                                                              201Sb                                              space (between proximal and distal module sets)                                                          201Sc                                              longitudinal axis          202                                                common lumen               203                                                branch vessel              203c                                               branch vessel section      203s                                               spine wire                 206                                                module                     207                                                virtual loop               208                                                cage-like tubular arrangement                                                                            210                                                vessel wall                211                                                virtual cylindrical surface                                                                              212                                                wire                       213                                                longitudinal segment module                                                                              214                                                cusp                       215                                                connector ring             219                                                ______________________________________                                    

The above components function in essentially the same manner as thosedescribed above in connection with the embodiments illustrated in FIGS.5 and 6. In the variation depicted in FIGS. 8-10, however, the proximalmodule set 201Sa of the second component stent 201S includes only asingle module 207 that is adapted to be placed within the singlecomplementary space 200sv in the proximal module set 201Pa of the firstcomponent stent 201P. In this embodiment, the L space of 200svcorresponds at least to the width LM of a module 207. The single moduleproximal set 20Sa is connected to the distal module set 201Sb by arelatively long spine wire 206. It should be noted that although thesecond component stent is shown in FIG. 9 as being bent in theconfiguration that it will assume when the two component stents areassembled (FIG. 10), the second component stent will be substantiallystraight when it is inserted into the previously placed first componentstent 201P.

FIGS. 11-14 illustrate further modifications to the stents describedabove in which the component stents are constructed to still furtherenhance the support that they provide for the blood vessel in the regionof the juncture of the vessels 203, 203c. To that end, the modules 207located immediately adjacent the side opening 300 (referred to as SF inFIGS. 5 and 6) are assembled from two serpentine wires, one of which(207') has a larger amplitude than the other (207"), that is, one of theserpentine wires has shorter longitudinal portions 214 than the other.The arrangement is apparent from FIG. 11 which illustrates the firstcomponent stent with its modules shown as spread out and lying in a flatplane. The serpentine wires that define the modules on each end of theside opening 300 (SF) are constructed from two wires having longitudinalportions 214 that are of different lengths and define a different pitch,as at 301' and 301". The wire that defines the side opening 300 (SF) isformed from the more closely pitched, shorter length serpentine wires.When the first component stent (FIG. 11) is in its cage-like, generallycylindrical configuration, the two modules that lie immediately adjacentthe side opening SF may be considered as each being formed from twoportions, each portion defining a virtual arcuate element 207', 207".The arcuate wire elements 207', 207" may be connected to each other byconnectors 219a. Additionally, a short longitudinal connector wire spine206a preferably is connected to the ring connectors 219a. Thearrangement of the spine wire 206, the short connector wire 206a and thesegments 207" cooperate to define a cage-like structure having a highdegree of local strength, particularly in the region of the side opening300 (SF) that will define the entry to the vessel branch 203c when thedevice is implanted. Additionally, the arrangement of fourfluoroscopically visible connector rings 219, 219a arranged inrectangular array about the opening 300 (SF) provides a means by whichthe position and orientation of the side opening can be verifiedfluoroscopically.

As shown in FIG. 12, the second component stent 201S includes a modulein close proximity to the juncture of the common and branch vessels inwhich the longitudinal portions 214p of the wire 13 are extended todefine a tongue-like configuration as described above in connection withthe embodiments of FIGS. 3, 5 and 6. This module associated with thesecond component stent may be formed in its entirety from a single wire,rather than forming it from two serpentine wires having longitudinalsegments 214 of different lengths.

It should be understood that the foregoing description of the inventionis intended merely to be illustrative thereof and that otherembodiments, modifications and equivalents will be apparent to thoseskilled in the art without departing from its principles.

What is claimed is:
 1. A method for forming a bifurcated stent within abody lumen having a common portion and first and second branchescommunicating with the common portion at a juncture, comprising thesteps of:providing a first tubular component stent open at each end,having a side opening between its ends, and being expandable radiallyfrom a low profile to an expanded configuration; providing a catheterhaving an expansion member at a distal end of the catheter and aguidewire duct having a guidewire port located between ends of theexpansion member to enable a distal end of a guidewire to extend out ofthe guidewire port; mounting a first component stent on the expansionmember with the side opening in registry with the guidewire port;advancing the assembly of the catheter and first component stent to thejuncture of the common portion and first and second branches of the bodylumen and with the side opening facing an entrance to the second branch,a proximal portion of the first component stent being disposed withinthe common portion of the body lumen and a distal portion of the firstcomponent stent being disposed in the first branch of the body lumen;operating the expansion member to expand the first component stentwithin the body lumen into engagement with an interior surface of thebody lumen; advancing a guidewire through the guidewire duct, theguidewire port and into the second branch of the body lumen; whilemaintaining the guidewire in its position in the second branch of thebody lumen, removing the catheter from the patient; advancing a secondcomponent stent in to the body lumen, guiding the second component stentby the guidewire to place at least a distal portion of the secondcomponent stent through the side opening of the first component stentand in the second branch of the body lumen; and expanding the secondcomponent stent into engagement with an interior surface of the bodylumen.
 2. A method as defined in claim 1 wherein the expansion membercomprises a balloon, the method further comprising folding a portion ofthe balloon about the distal portion of the guidewire duct beforemounting the first component stent on the balloon, the balloon foldingbeing such as to maintain the guidewire port exposed.
 3. A method asdefined in claim 2 wherein the step of folding the balloon comprisesmaking at least one on each side of the guidewire duct.
 4. A method asdefined in claim 1 wherein the expansion member comprises an electricalresistance heater and wherein the step of mounting the first componentstent on the catheter comprises locating the heater between a shaft ofthe catheter and the guidewire duct.
 5. A method as defined in claim 1wherein the catheter includes a shaft that includes a guidewire lumenopen at the distal tip of the shaft and where the step of advancing theassembly of the catheter and first component stent comprisespreliminarily extending the guidewire from the distal end of thecatheter and manipulating the guidewire to provide a path for advancingand guiding the catheter to the intended location of stent placement. 6.A method for placing a component stent of a bifurcate stent assemblycomprising the steps of:mounting the component stent on a deliverydevice having an expansion member at a distal end of the deliverydevice, the component stent have a side opening between a distal end anda proximal end of the component stent; interposing a guidewire ducthaving a guidewire exit port between the expansion member of thedelivery device and the stent, with the guidewire duct having aguidewire exit port in registry with the side opening of the componentstent; advancing the assembled delivery device and component stentthrough a body lumen to a region of a juncture of a common portion andbranches of the body lumen with the side opening and the guidewire exitport facing one of the branches.
 7. A component stent for placement at abifurcated region of a body lumen comprising:an elongate tube-definingmember having a proximal section and a distal section, each of theproximal and distal sections including at least one radially expandablemodule; and a side opening defined between a distal module of theproximal section and a proximal module of the distal section, wherein aportion of either the distal module of the proximal section or theproximal module of the distal section extends towards and is in closeproximity to either the proximal module of the distal section or thedistal module of the proximal section to provide substantiallycontinuous support of the body lumen, and wherein the modules are formedfrom wire arranged in a serpentine pattern including a plurality ofelongate segments alternated with shorter connective bends, at leastsome of the elongate segments on at least one of the distal module ofthe proximal section or the proximal module of the distal section beinglonger than other elongate segments of said at least one module.
 8. Acomponent stent as defined in claim 7 wherein the elongate segments ofsaid at least one module which are disposed laterally of the sideopening are longer than the other elongate segments of said at least onemodule.
 9. A component stent as defined in claim 7 wherein the elongatesegments are connected to each other at cusps and where the cusps of thedistal module of the proximal portion and the proximal module of thedistal portion are disposed in close proximity to each other.
 10. Acomponent stent as defined in claim 7 wherein the elongate segments areconnected to each other at cusps and where the cusps of one of thedistal module of the proximal portion or the proximal module of thedistal portion overlaps and extends beyond the cusps of the other of thedistal module of the proximal portion or the proximal module of thedistal portion.
 11. A bifurcated stent comprising:a first componentstent and a second component stent, each of which includes a pluralityof modules arranged in a sequence to define a generally tubularconfiguration; and a side opening defined between a pair of sequentiallydisposed modules of the first component stent, wherein the secondcomponent stent extends through a portion of the first component stentand projects laterally through the side opening, and wherein said pairof modules on the first component stent have side portions disposedlaterally of the side opening that extend toward and into proximity witheach other, and wherein each module of said pair of modules definingsaid side opening is formed from wire arranged in a serpentine patternincluding elongate segments serially connected to each other by cusps,the elongate segments of said pair of modules being arranged so thatsome of the cusps of one module of said pair of modules are disposed inclose proximity to some of the cusps of the other module of said pair ofmodules, and wherein some of the cusps of one module of said pair ofmodules overlap and extend beyond at least one cusp of the other moduleof said pair of modules.
 12. A catheter for delivering a component stentof a bifurcated stent in which the component stent includes a sideopening comprising:an elongate flexible shaft; an expansion membermounted to a distal end of the shaft; and an elongate guidewire ductextending longitudinally of the shaft, the guidewire duct having adistal end exposed externally of the expansion member and defining aguidewire exit port at a location disposed longitudinally between theends of the expansion member, the guidewire exit port being configuredto enable a guidewire to emerge from the guidewire duct in a directionthat extends at an angle to the longitudinal axis of the catheter.
 13. Adelivery catheter as defined in claim 12 wherein the catheter shaft iscoaxial and includes an inner tube and an outer tube.
 14. A deliverycatheter as defined in claim 12 wherein the stent is adapted to expandupon the application of heat and where the expansion member comprisesmeans carried by the catheter for applying heat to the component stent.15. A delivery catheter as defined in claim 12 wherein the expansionmember comprises a balloon.
 16. A component stent of a bifurcated stentcomprising:a plurality of loop-like modules connected sequentially toand along a spine to define a generally tubular configuration; at leasttwo of the modules being formed from wire arranged in a serpentinepattern to include elongate segments connected to each other at cusps;and a pair of sequentially disposed modules defining a side opening;wherein at least one of said pair of modules includes elongate segmentsof different lengths.
 17. A component stent as defined in claim 16wherein said at least one module has a pair of serpentine wires, one ofsaid pair of serpentine wires having elongate segments which are longerthan those of the other of said pair of serpentine wires, the serpentinewire with shorter elongate segments being connected to an end of theserpentine wire with longer elongate segments.
 18. A component stent asdefined in claim 17 wherein the serpentine wire with shorter elongatesegments defines the axial ends of the side opening.
 19. A componentstent as defined in claim 17 wherein the serpentine wire with longerelongate segments defines a portion of the component stent disposedlaterally of the side opening.
 20. A component stent as defined in claim18 whereinone end of the serpentine wire with shorter elongate segmentsis connected to the spine, and the other end of the serpentine wire withshorter elongate segments is connected to an end of the serpentine wirewith longer elongate segments.
 21. A component stent as defined in claim20 wherein the serpentine wire with the shorter elongate segments isconnected to the spine at a connector that has a substantially largerradiographic mass than that of the wire.
 22. A component stent asdefined in claim 21 wherein the serpentine wire with the shorterelongate segments is connected to the serpentine wire with the longerelongate segments at a connector having substantially greaterradiographic mass than the wires.
 23. A component stent as defined inclaim 26 wherein the connectors that connect the serpentine wire withthe shorter elongate segments to the spine and the serpentine wire withthe longer elongate segments define a generally rectangular pattern thatdefines the comers of the side opening.
 24. A component as defined inclaim 26 further comprising:a short connector wire extended between ajunction of said serpentine wire with shorter elongate segments and saidserpentine wire with longer elongate segments of one of said pair ofmodules and a junction of said serpentine wire with shorter elongatesegments and said serpentine wire with longer elongate segments of theother of said pair of modules.
 25. A component stent as defined in claim17 where the pitch with respect to a longitudinal axis of the stent ofthe serpentine wire with shorter elongate segments is less than thepitch with respect to a longitudinal axis of the stent of the serpentinewire with longer elongate segments.
 26. A component stent as defined inclaim 16, wherein each module of said pair of modules includes a pair ofserpentine wires, one of said pair of serpentine wires having elongatesegments which are longer than those of the other of said pair ofserpentine wires, the serpentine wire with shorter elongate segmentsbeing connected at one end to the support wire by a connector and atanother end to an end of the serpentine wire with longer elongatesegments by a connector.